A will, a power of attorney, a health care directive: which does what

A will says what happens to your property after you die and who looks after your children. It does nothing while you are alive (sample note).
A power of attorney lets someone you trust deal with your money and property if you cannot. A health care directive says who makes medical decisions for you, and what you would want.
Most people sign all three at the same appointment. This note is general information; the rules differ from state to state, so ask about your own case.